In the modern world, hand-held communication devices such as mobile phones, personal handyphone system (PHS), car phones, and pocket beepers have become an integral part of people's lives and prominent media of communication. Hand-held communication devices provide multiple modes through which the parties can communicate with each other. Such modes include two-way communication modes such as direct voice conversation between the parties over the phone and one-way communication modes such as Short Message Service (SMS).
Hand-held devices typically have limited textual input options due to their small sizes, which can support only small keyboards having limited number of keys. For instance, a basic model of a mobile phone has 21 keys, wherein 12 keys are present for entering text inputs (present in the form of a 3*4 matrix), 2 keys are used for communication functionality (Red and Green buttons), 3 keys are used for selection options, and 4 keys (Up, Down, Left, Right) are used for navigation purposes. These small set of keys are expected to support large alphabet sets in one or more languages for applications such as text messaging. For instance, while typing a text message (a SMS), a number of characters in multiple forms such as in upper and lower cases, numbers and special characters, symbols, and other options are needed. If we take the case of English, it is common to see a set of characters of the English alphabet printed on each of the keys. Each key refers to more than one alphabet, leaving it ambiguous to which alphabet the user may have had in mind to input. For instance, in most mobile phones, the key “2” refers to “abc” and key “7” refers to “pqrs”. This kind of keypad is therefore called an ambiguous keypad in the related scientific literature. Multiple technologies have been introduced in recent times for text input mechanisms for touch-typable devices.
Multitap Technology:
Multitap is the first popular form of typing in English using an ambiguous keypad scheme, which depends on the user rapidly pressing any of the keys to refer to a particular key in the list of alphabets shown on it. For example, to type “b”, a user would have to tap the Key 2 twice, and to type “s”, the user would press the key 7 four times. This is called mutlitapping and is a cumbersome, slow, and error prone process, as the user is susceptible to press the keys more number of times or less number of times than required. It is not very usable for the old or the ill because it relies on the user pressing the key at a minimum acceptable rate of one key press within a short duration (1 to 2 seconds), also referred to as multitap timeout. The above rate cannot even be slowed down because that would result in slowing down of the whole system. The multiple tap timeout is applicable in cases where words that have consequent alphabets printed on the same key, need to be typed. For example if the word “ORDER” needs to be typed, D and E being from the same key “3”, would need a delay between the two inputs D and E to count as separate inputs and not part of the same multitap, which, on the other hand, would result in three consequent taps and hence an input of F. Single tap for D and two taps for E and a gap in the middle is therefore needed while entering “ORDER”, which in effect would have a multitap timeout of a fixed duration for each input. Increasing this time out period slows down the whole text entry system. A multitap kill button mentioned in certain literatures would involve the pressing of yet another button to override the multitap timeout duration.
Dictionary Matches:
The next form to grow popular removes the need of multitapping. This technology asks the user to type in the word regardless of the ambiguities and the machine tries to remove the ambiguity by referring to an inbuilt dictionary to find a likely match. For example, if a user intends to type “MOTHER”, he/she would go on pressing the keys 6-6-8-4-3-7. Since each of these keys (6-6-8-4-3-7) maps to three or more possible characters, it results in a large set of possible inputs (3*3*3*3*3*4=324 distinct word formations in the case of 6-6-8-4-3-7) that could have been intended. The software in the machine refers to the dictionary to prune down the possible sets of words only to the ones that are found in the dictionary.
This dictionary based technology works under the assumption that at most times the user would be typing in valid words from the English dictionary. This is not entirely true because of the prevalence of non dictionary words, proper nouns, names of places, people, numbers, shortened words, and abbreviations, etc, which are particularly common in personal messages sent from one to another over mobile phones due to the nature of the application. The words that are not in the dictionary have to be entered manually by the user through the same multitap technology described above and hence the user has to frequently change the mode from dictionary matching mode to manual entry mode. The process is cumbersome and a large percentage of users are unfamiliar as to how it is done. They have preferred to fall back on multi-tapping to type in all their texts. Also the total number of words in English is over 600,000 (Oxford English Dictionary 2'nd Edition) and since it is not considered feasible or desirable to include such a large dictionary on the typable devices due to cost, complexity and other limitations, a limited dictionary of only about 30,000 words (or 5%) is what is found in most implementations. In areas outside the English speaking locales, as in Malaysia or India, where the English keypad is the one which is used, the users are left to multi-tapping for all their words.
Another related issue that arises out of this strategy is called collision or dictionary collision. This refers to situations where two or more words in the dictionary refer to the same key sequence combination. For example, the 3 key sequence (2-6-9) refers to “any”, “boy”, “cow”, “box”-four common words; and other less common words. In fact, for almost every word entered there is likely to be other collision words. Even though the other collision words are less likely to be present, one does come across words which were not intended to be used. A few common collisions that do occur frequently are (me, of), (kiss, lips), (good, home, gone). The list is large and gets larger when the dictionary size is made bigger, which is one of the reasons why the size of the dictionary is limited by the manufacturers. For every such collision, it is left to the user to detect the collision and to choose the right word. A means is generally provided to the user to choose from a list of possible other words, from a drop down menu or some other means on the input interface which involves a few extra key presses from the user.
In most cases, the user is looking at the printed alphabets on the keypad while typing and not at the screen, leaving the undesired collision words to go unnoticed on the screen. This results in the user having to review all the entered text before sending and if there is a collision word, the user has to manually move the cursor letter by letter over the entire text to make that small change.
Chording:
Chording is another method to enter text in which more than one keys are pressed at the same time or in some implementations in quick succession, quite like the Shift key used on a standard PC keyboard to create the distinction between upper and lower case letters and other symbols. In some cases the Control key, Alt key, Function keys are also used in a similar fashion. Such a strategy has also been used in handheld devices to increase the input choices from the limited keypad but have failed to become popular.
Mixed Strategy of Multitap:
There have also been other solutions, such as those in which Multitap and a likelihood prediction have been mixed. This approach merely changes the order in which the letters in the ambiguous keypad are offered after each multi-tap, the most likely letters being offered first, instead of the default order. This can reduce the total number of multi-taps required in an overall statistical sense. But a constant disambiguation role on the part of the user is necessitated and this is cumbersome. For instance, in case a user wants to type the word “WHICH”, after typing “W”, the technology shall, based on the statistical likelihood comparison between WG, WH, WI, give one of the letters as the output when the key “4” is pressed. In case the letter “I” has higher statistical likelihood, the user will have to select the key again (based on the mechanism of letter change or letter disambiguation) and then select letter “H”, which leaves space for rework by the user and leads to more time consumption on ambiguous keypads. Also users of multitap who are sometimes capable of typing without looking at the screen now need to look at the screen to know which letter was predicted by the system.
All of these interruptions and necessary interventions expected from the user limit the usability currently offered for text inputs and therefore the users prefer to use the cumbersome but more straightforward multi-tap system to enter their text even when some or the other kind of dictionary matching scheme is supported on the majority of phones in the market.
There have been variations in the above described technologies in which there are larger number of keys to reduce ambiguation (assigning two letters to each key instead of three or four). There have been others who have theorized about the possibility of a more optimal choice of characters assigned to each key of the keypad to reduce collisions and thus reduce the number of times disambiguation that is required from the user. But no such keypads find popular usage for reasons of usability and intuitiveness. The most widely used form of keypad continues to be the one with 12 keys for entering the text. It is also impossible for printed disambiguation keypads to support multiple languages because there isn't that much of space on the face of a key.
There is therefore a need for systems and methods for text input that remove the ambiguity that is seen while typing with the existing keypads, a means to support many languages on the same keyboard and increase the speed with which the textual inputs can be given to multiple touch-typable devices.